1. Field of the Invention
The present invention is related to a method for driving a plasma display panel, and more particularly, to a method for driving a plasma display panel, in which a reset discharge that makes all wall charge states of cells uniform is induced to occur at a position under a black matrix during a reset period for improving a contrast.
2. Background of the Related Art
The plasma display panel and LCD(Liquid Crystal Display) are spotlighted as next generation displays of the greatest practical use, and, particularly, the plasma display panel has wide application as a large sized display, such as an outdoor signboard, a wall mounting type TV, a display for a movie house because the plasma display panel has a higher luminance and a wide angle of view than the LCD.
As shown in FIG. 1A, a general plasma display panel of triode surface discharge type has an upper substrate 10 and a lower substrate 20 bonded together facing each other. FIG. 1B illustrates a section of a plasma display panel shown in FIG. 1A, wherein the lower substrate 20 is shown with a face of the lower substrate 20 rotated by 90xc2x0 for convenience of explanation.
The upper substrate 10 is provided with scan electrodes 16 and 16xe2x80x2 and sustain electrodes 17 and 17xe2x80x2 formed in parallel, and a dielectric layer 11 and a protection film 12 each coated on the scan electrodes 16 and 16xe2x80x2 and the sustain electrodes 17 and 17xe2x80x2 in succession, the lower substrate 20 is provided with address electrodes 22, a dielectric film 21 formed on an entire surface of the substrate inclusive of the address electrodes 22, barriers 23 formed on the dielectric film 21 between the address electrodes 22, and a fluorescent material 24 coated on surfaces of the barrier 23 and the dielectric film 21 in each of the discharge cells, and a space between the upper substrate 10 and the lower substrate 20 is filled with a mixture of inert gases, such as helium or xenon, at a pressure in a range of 400 to 500 Torr, to form a discharge region. In general, the inert gas filled in the discharge space in a DC plasma display panel is a mixture of helium and xenon, and the inert gas filled in the discharge space in an AC plasma display panel is a mixture of neon and xenon.
As shown in FIGS. 2A and 2B, the scan electrodes 16 and 16xe2x80x2 and the sustain electrodes ma 17 and 17xe2x80x2 are transparent electrodes 16 and 17 or bus electrodes 16xe2x80x2 and 17xe2x80x2 of a metal for increasing a light transmittivity of the discharge cells. FIG. 2A illustrates a plan view of the sustain electrodes 17 and 17xe2x80x2 and the scan electrodes 16 and 16xe2x80x2, and FIG. 2B illustrates a section of the sustain electrodes 17 and 17xe2x80x2 and the scan electrodes 16 and 16xe2x80x2. The bus electrodes 16xe2x80x2 and 17xe2x80x2 have a discharge voltage provided thereto from an external driver IC, and the transparent electrodes 16 and 17 have the discharge voltage provided to the bus electrodes 16xe2x80x2 and 17xe2x80x2 provided thereto, for causing a discharge between adjacent transparent electrodes 16 and 17. The transparent electrode 16 and 17 has a total width of approx. 300 xcexcm, and formed of indium oxide or tinoxide, and the bus electrode 16xe2x80x2 and 17xe2x80x2 has a thin film of three layers of Crxe2x80x94Cuxe2x80x94Cr. The but electrode 16xe2x80x2 and 17xe2x80x2 has a line width which is approx. ⅓ of a line width of the transparent electrode 16 and 17.
FIG. 3 illustrates a wiring for the scan electrodes Smxe2x88x921, Sm, Sm+1, - - - , Snxe2x88x921, Sn, Sn+1 and the sustain electrodes Cmxe2x88x921, Cm, Cm+1, - - - , Cnxe2x88x921, Cn, Cn+1, formed on the upper substrate, wherein the scan electrodes are insulated from one another, while all of the sustain electrodes are connected in parallel. Particularly, an area shown by dotted line in FIG. 3 denotes an effective area in which an image is displayed, and the other area denotes a non-effective area in which no image is displayed. The scan electrodes disposed in the non-effective area are called dummy electrodes 26, of which number is not limited, especially.
The operation of the aforementioned AC plasma display panel of a triode surface discharge type will be explained with reference to FIGS. 4Axcx9c4D.
Referring to FIG. 4A, upon application of a driving voltage between the address electrode and the scan electrode, an opposed discharge takes place between the address electrode and the scan electrode. This-opposed discharge produces ions as the inert gas filled in the discharge cell is excited momentarily and transited to a ground state, and a portion of ions, or atoms in a quasi-excited state, generated in this time, is collided at surfaces of the protection layer as shown in FIG. 4B. These electron collision cause emission of secondary electrons from surfaces of the protection layer. The secondary electrons collide at a plasma state gas, which spreads the discharges. Upon finish of the opposed discharge between the address electrode and the scan electrode, wall charges of opposite polarities are formed at respective protection layer surfaces of the address electrode and the scan electrode as shown in FIG. 4C. And, as shown in FIG. 4D, if the driving voltage provided to the address electrode is cut off while the discharge voltages of opposite polarities are kept provided to the scan electrodes and the sustain electrodes, a surface discharge caused by a potential difference between the scan electrodes and the sustain electrodes takes place in a discharge region of surfaces of the dielectric layer and the protection layer. These opposed discharge and the surface discharge causes electrons present in the discharge cell to collide onto the inert gas in the discharge cell, to excite the inert gas in the discharge cell to emit a UV ray with a wavelength of 147 nm in the discharge cell. The UV ray collides onto the fluorescent material coated on the address electrode and the barrier, to excite the fluorescent material, to emit a visible light, that forms an image on a screen. One pixel has a discharge cell of a red fluorescent material, a discharge cell of a green fluorescent material, and a discharge cell of a blue fluorescent material. By controlling a number of discharges in each of the discharge cells, the plasma display panel implements a gradation of an image. In this instance, the discharges taken place in each of the discharge cells consists of the address discharge for initiating a discharge, a sustain discharge for sustaining a discharge of the discharge cell, and an erase discharge for stopping the discharge of the discharge cell. Though there are a sub-field method and a sub-frame method in methods for driving a plasma display panel for implementing an image using those address discharge, the sustain discharge, and the erase discharge, a driving method widely used generally is an ADS(Address Display Separating) sub-field method in which an address discharge period and a sustain discharge period are separated. In order to implement a 2xc3x97 gradation in the ADS sub-field method, one frame of image is divided into Y sub-field frames of images before displaying the image, and an external video data is digitized into an X bit digital video data before the external video data is provided to the plasma display panel(where, Xxe2x89xa6Y). And, each sub field frame consists of a reset period, an address period, and a sustain period. Identical reset period and address period are assigned to every sub field. Different sustain periods are assigned to the sub fields depending on a weighted value of bits of the digital video data to be displayed in the address period. Therefore, a combination of the sub fields implements a gradation of the image. As an example, as shown in FIG. 5, when one frame is divided into 8 sub fields(SF1, SF2, SF3, SF4, SF5, SF6, SF7 and SF8), and luminances of 1, 2, 4, 8, 16, 32, 64, and 128 are corresponded, a combination of some of the sub fields facilitates to implement a gradation data with a gradation ranging 0xcx9c255.
In the meantime, because there are cells discharged, and cells not discharged in a prior frame coexistent in the reset period, all the discharge cells should be discharged for making all wall charge states uniform. To do this, a reset pulse Vw is applied to the sustain electrode C as shown in FIG. 6. Since a reset pulse voltage Vw is higher than a discharge starting voltage Vf between the scan electrode Sm, Smxe2x88x921, Snxe2x88x921 and Sn and the sustain electrode, a discharge takes place at an rising edge, which is maintained for 5 xcexcsxcx9c15 xcexcs, to form adequate wall charges. These wall charges cause discharges again at a falling edge of the reset pulse, to neutralize the wall charges, that makes the wall charge states uniform.
However, the non-uniform discharge voltages between discharge cells coming from thickness differences of non-uniform fluorescent material layers, and pressure differences of the inert gas, which exist inevitably between the discharge cells, cause the wall charges to remain even after application of the reset pulse. There is an erase period in which erase pulses are applied to the scan electrodes Sm, Smxe2x88x921, Snxe2x88x921, Sn, - - - within the effective area after the reset period in which reset pulses are applied for erasing the remained wall charges. In the erase period, small amounts of wall charges remained at the sustain electrodes are neutralized, and erased in succession by the erase pulses. Then, during the address period, a scan pulse is applied to the scan electrodes one by one in succession, and a wall charge is formed as a cell of a designated pixel is discharged on application of a data pulse to the address electrode, and, during the sustain period, a luminance of the pixel having a discharge occurred during the address period is sustained as a sustain pulse proportional to a relative luminance ratio of the scan electrode and the sustain electrode is provided. Though the foregoing reset discharge is not required for implementation of gradation in the related art sub field driving method, the reset discharge is essential for a stable discharge. However, in the related art sub field method, the exposure of visible lights from the reset discharge increases a luminance of the black image, which reduces a contrast of the image.
Accordingly, the present invention is directed to a method for driving a plasma display panel that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for driving a plasma display panel, which can cut off an exposure of a visible light from a reset discharge, for reducing a luminance of a black image in a plasma display panel, that improves a contrast of an image.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for driving a plasma display panel includes the steps of (1) conducting an erase discharge at a region under the first black matrix formed between the odd numbered scan electrode lines and the even numbered sustain electrode lines, and (2) conducting an erase discharge at a region under the second black matrix formed between the even numbered scan electrode lines and the odd numbered sustain electrode lines.
The method for driving a plasma display panel further includes the steps of (3) maintaining a potential difference between the odd numbered scan electrode lines and the odd numbered sustain electrode lines to a level which causes no discharge during the time when the erase discharge is taken place between the odd numbered scan electrode lines and the even numbered sustain electrode lines, and (4) maintaining a potential difference between the even numbered scan electrode lines and the even numbered sustain electrode lines to a level which causes no discharge during the time when the erase discharge is taken place between the even numbered scan electrode lines and the odd numbered sustain electrode lines.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.